DVD+RW and DVD-RW will die after a few months, used or not.
How long is a "few months" is the question, right? Well, it all comes down to how good the media is.
Most of my INFODISCA1 DVD+RW are dead now. I had about 75 of them in 2004, and as of today, most of them are goners. I threw away at least 20 of them within 6 months, the rest got pitched out every 3 months after that.
My SONY DVD+RW all went pretty quick too, in fact 2 out of 10 were dead the day I bought them. At least 2-3 of the 10 Fuji discs I bought last summer are now toast as well.
RW media is not like -R or +R media. DVD-R and DVD+R use dyes. RW media is not using dye, it uses phase-change crystals.
You can almost always see a bad RW disc with the naked eye. It develops craters in the materials (as in moon craters). Some are tiny, pin-head sized, some are a whole 1mm across, so look carefully.
In general, DVD-RW lasts a lot longer thatn DVD+RW.
I have been using TDK (TDK), Maxell (MXL), Sony (SONY), Fuji (MKM) and Pioneer (PVC) DVD-RW in my JVCs since 2004. All of my PVC and MKM discs are fine. I've lost a few of the others in the past 2 years, maybe 5 out of 30. I currently have 45 DVD-RW discs, left from the 50 I bought initially.
On the flipside, I got a lot of free PRINCO and RITEK DVD-RW media back in 2002-2003, all of it died after 2-3 uses. I have 1 Memorex-branded RITEK DVD-RW that still works, but I try to never rely on it for something important.
These should be good (excellent price):